85 lines
3.3 KiB
Markdown
85 lines
3.3 KiB
Markdown
---
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title: Container Command and Arguments
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---
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{% capture overview %}
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In the configuration file for a Container, you can set the `command` and `args`
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fields to override the default Entrypoint and Cmd of the the Container's image.
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{% endcapture %}
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{% capture body %}
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## Container entry points and arguments
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The configuration file for a Container has an `image` field that specifies
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the Docker image to be run in the Container. A Docker image has metadata that includes
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a default Entrypoint and a default Cmd.
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When Kubernetes starts a Container, it runs the image's default Entrypoint and
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passes the image's default Cmd as arguments.
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If you want override the image's default Entrypoint and Cmd, you can use the
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`command` and `args` fields in the Container's configuration.
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* The `command` field specifies the actual command run by the Container.
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* The `args` field specifies the arguments passed to the command.
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This table summarizes the field names used by Docker and Kubernetes.
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| Description | Docker field name | Kubernetes field name |
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|----------------------------------------|------------------------|-----------------------|
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| The command run by the container | Entrypoint | command |
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| The arguments passed to the command | Cmd | args |
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Here's an example of a configuration file for a Pod that has one Container.
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{% include code.html language="yaml" file="commands.yaml" ghlink="/docs/concepts/configuration/commands.yaml" %}
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When Kubernetes starts the Container, it runs this command:
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```shell
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printenv HOSTNAME KUBERNETES_PORT
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```
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When you override the default Entrypoint and Cmd, these rules apply:
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* If you do not supply `command` or `args` for a Container, the defaults defined
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in the Docker image are used.
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* If you supply a `command` but no `args` for a Container, only the supplied
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`command` is used. The default EntryPoint and the default Cmd defined in the Docker
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image are ignored.
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* If you supply only `args` for a Container, the default Entrypoint defined in
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the Docker image is run with the `args` that you supplied.
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* If you supply a `command` and `args`, the default Entrypoint and the default
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Cmd defined in the Docker image are ignored. Your `command` is run with your
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`args`.
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Here are some examples:
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| Image Entrypoint | Image Cmd | Container command | Container args | Command run |
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|--------------------|------------------|---------------------|--------------------|------------------|
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| `[/ep-1]` | `[foo bar]` | <not set> | <not set> | `[ep-1 foo bar]` |
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| `[/ep-1]` | `[foo bar]` | `[/ep-2]` | <not set> | `[ep-2]` |
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| `[/ep-1]` | `[foo bar]` | <not set> | `[zoo boo]` | `[ep-1 zoo boo]` |
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{% endcapture %}
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{% capture whatsnext %}
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* [Defining a Command and Arguments for a Container](/docs/tasks/configure-pod-container/define-command-argument-container/)
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* [Running Commands in a Container with kubectl exec](/docs/user-guide/getting-into-containers/)
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* [Container](/docs/api-reference/v1/definitions/#_v1_container)
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* [Docker Entrypoint field](https://docs.docker.com/engine/reference/builder/)
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{% endcapture %}
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{% include templates/concept.md %}
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